Scielo RSS <![CDATA[Brazilian Journal of Chemical Engineering]]> http://www.scielo.br/rss.php?pid=0104-663220070003&lang=en vol. 24 num. 3 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[<B>Maintenance of penicillin G acylase expression by <I>B. megaterium</B></I>: <B>preservation methods and activity recovery</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300001&lng=en&nrm=iso&tlng=en This work reports the influence of different culture preservation methods on the production of penicillin G acylase (PGA) by Bacillus megaterium ATCC 14945. The initial stock culture, presenting PGA activity of 97 IU l-1, was preserved for two years using different procedures: monthly subculturing and storage in refrigerator (S), freeze-drying using skim milk 10%, plus inositol 5% as cryoprotectors (L1), freeze-drying using sucrose 7%, plus peptone 7% (L2), and freezing with glycerol 10% (F). After cultivations at standard operational conditions, different values of enzyme activity were obtained: 56 IU l-1 for monthly subculturing (S), 15-41 IU l-1 for freeze-dried cells and frozen spores. All the tested methods have failed in preserving the PGA expression. Among all tested cultures, S presented the highest specific activity, and was used to prepare a standard inoculum in cryovials (-50ºC, frozen spores in a 20% glycerol solution). By cultivation of this inoculum under different conditions, it was found that PGA activity raised to 128 IU l-1 when 0.4 g l-1 of salts was added to the medium. <![CDATA[<B>Recombinant human proinsulin from transgenic corn endosperm</B>: <B>solvent screening and extraction studies</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300002&lng=en&nrm=iso&tlng=en Recombinant pharmaceutical proteins are being produced in different systems such as bacteria and mammalian cell cultures. The use of transgenic plants as bioreactors has recently arisen as an alternative system offering many practical and economic advantages. However, finding an optimum strategy for the downstream processing (DSP) of recombinant proteins from plants still remains a challenge. In this work, we studied the extraction of recombinant human proinsulin (rhProinsulin) produced in the endosperm of transgenic corn seeds. An efficient extraction solvent was selected and the effects of temperature, solvent-to-solid ratio, time, and impeller rotational speed on the extraction were evaluated using an experimental design. After an extraction kinetics study, temperature was further evaluated to maximize rhProinsulin concentration in the extracts and to minimize the native corn components carbohydrates, phenolic compounds, and proteins. A high efficiency condition for extracting rhProinsulin with the selected solvent - 50 mM sodium bicarbonate buffer pH 10.0 and 5 mM DTT - was an extraction time of 2 h at a solvent-to-solid ratio of 10:1 and 25º C. The maximum rhProinsulin concentration in the extracts at that condition was 18.87 mg l-1 or 0.42% of the total soluble protein. These values are within the range in which the production of pharmaceutical proteins in plants can be competitive with other expression systems. The results presented provide information for the development of an additional production platform for the hormone insulin. <![CDATA[<B>Characterization of chemically modified chitosan microspheres as adsorbents using standard Proteins (bovine serum albumin and lysozyme)</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300003&lng=en&nrm=iso&tlng=en Chitosan microspheres with a mean size of 140 &plusmn; 119 µm were produced by the spray and coagulation methods. The microspheres were chemically modified using the following routes: a) crosslinking with glutaraldehyde b) crosslinking with epychlorohydrin and c) acetylation. For investigation of their ability as adsorbents, the following standard proteins were chosen as adsorbates: bovine serum albumin - BSA (pI = 4.8 and MW = 66 kDa) and lysozyme (pI = 11 and MW = 14 kDa). The adsorption experiments were performed using a static method. The adsorption media and equilibrium concentration of adsorbates were varied in the ranges of pH 4-11 and 0.07-0.70 mg.ml-1, respectively. The maximum adsorption capacities (q m) and the constant of the Langmuir model (Ks) were shown to be dependent on charge interactions and on the kind of treatment performed on chitosan microspheres. The satisfactory fit of a kinetic model to the experimental data shows that the step that controls the adsorption kinetics is probably the initial adsorbate transport. <![CDATA[<B>Simulation of NaCl and KCl mass transfer during salting of Prato cheese in brine with agitation</B>: <B>a numerical solution</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300004&lng=en&nrm=iso&tlng=en The association of dietary NaCl with arterial hypertension has led to a reduction in the levels of this salt in cheeses. For salting, KCl has been used as a partial substitute for NaCl, which cannot be completely substituted without affecting product acceptability. In this study a sensorially adequate saline solution (NaCl/KCl) was simultaneously diffused during salting of Prato cheese in brine with agitation. The simultaneous multicomponent diffusion during the process was modeled with Fick’s second generalized law. The system of partial differential equations formed was solved by the finite element method (FEM). In the experimental data concentration the deviation for NaCl was of 7.3% and for KCl of 5.4%, both of which were considered acceptable. The simulation of salt diffusion will allow control and modulation of salt content in Prato cheese, permitting the prediction of final content from initial conditions. <![CDATA[<B>Comparison of turbulent particle dispersion models in turbulent shear flows</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300005&lng=en&nrm=iso&tlng=en This work compares the performance of two Lagrangian turbulent particle dispersion models: the standard model (e.g., that presented in Sommerfeld et al. (1993)), in which the fluctuating fluid velocity experienced by the particle is composed of two components, one correlated with the previous time step and a second one randomly sampled from a Wiener process, and the model proposed by Minier and Peirano (2001), which is based on the PDF approach and performs closure at the level of acceleration of the fluid experienced by the particle. Formulation of a Langevin equation model for the increments of fluid velocity seen by the particle allows capturing some underlying physics of particle dispersion in general turbulent flows while keeping the mathematical manipulation of the stochastic model simple, thereby avoiding some pitfalls and simplifying the derivation of macroscopic relations. The performance of both dispersion models is tested in the configurations of grid-generated turbulence (Wells and Stock (1983) experiments), simple shear flow (Hyland et al., 1999) and confined axisymmetric jet flow laden with solids (Hishida and Maeda (1987) experiments). <![CDATA[<B>A study of particle motion in rotary dryer</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300006&lng=en&nrm=iso&tlng=en The purpose of this work was to study the performance of a rotary dryer in relation to number of flights. In this work an equationing was proposed to calculate the area used by the solids in two-segment flights of with any angle between the segments. From this area, the flight holdup and the length of fall of the particles were calculated for different angle positions and the results obtained were compared to experimental values. The results show an increase in dryer efficiency with the increase in number of flights up to a limit value, for ideal operational conditions. The experimental data on average residence time were compared to results obtained by calculations using equations proposed in the literature. The equation proposed for predicting flight holdup and length of fall of particles generated very accurate estimations. <![CDATA[<B>Natural convection heat transfer in partially open enclosures containing an internal local heat source</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300007&lng=en&nrm=iso&tlng=en A numerical study was conducted to investigate steady heat transfer and flow phenomena of natural convection of air in enclosures, with three aspect ratios (H/W = 1, 2, and 4), within which there is a local heat source on the bottom wall at three different positions, Wh. This heat source occupies 1% of the total volume of the enclosure. The vertical walls in the enclosures are insulated and there is an opening on the right wall. The natural convection is influenced by the difference in temperature between the left and right walls, represented by a Rayleigh number (Ra e), and by local heat source, represented by a Rayleigh number (Ra i). Numerical simulations were performed for several values of the Rayleigh number ranging between 10³ and 10(6), while the intensity of the two effects - the difference in temperature on the vertical walls and the local heat source - was evaluated based on the Ra i/Ra e ratio in the range between 0 and 2500. The analysis proceeds by observing variations in the streamlines and isotherms with respect to the different Ra e, R ratios, aspect ratios, of the radius and positions of the local heat source. The average Nusselt numbers on the hot and cold walls are influenced by different values of the parameters R, Ra e, Wh, and H/W. Results show the presence of different flow patterns in the enclosures studied. Thus, the flow and heat transfer can be controlled by external heating, and local heat source. <![CDATA[<B>The effect of vibration on bed voidage behaviors in fluidized beds with large particles</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300008&lng=en&nrm=iso&tlng=en The effects of vibration parameters, operating conditions and material properties on bed voidage were investigated using an optical fiber probe approach in a vibrating fluidized bed with a diameter of 148 mm. Variables studied included frequency (0-282 s-1), amplitude (0 mm-1 mm), bed height (0.1 m-0.4 m) as well as four kinds of particles (belonging to Geldart's B and D groups). The axial and radial voidage distribution with vibration is compared with that without vibration, which shows vibration can aid in the fluidization behaviors of particles. For a larger vibration amplitude, the vibration seriously affects bed voidage. The vibration energy can damp out for particle layers with increasing the bed height. According to analysis of experimental data, an empirical correlation for predicting bed voidage, giving good agreement with the experimental data and a deviation within &plusmn;15%, was proposed. <![CDATA[<B>Discretisation of the non-linear heat transfer equation for food freezing processes using orthogonal collocation on finite elements</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300009&lng=en&nrm=iso&tlng=en The freezing process is considered as a propagation problem and mathematically classified as an "initial value problem." The mathematical formulation involves a complex situation of heat transfer with simultaneous changes of phase and abrupt variation in thermal properties. The objective of the present work is to solve the non-linear heat transfer equation for food freezing processes using orthogonal collocation on finite elements. This technique has not yet been applied to freezing processes and represents an alternative numerical approach in this area. The results obtained confirmed the good capability of the numerical method, which allows the simulation of the freezing process in approximately one minute of computer time, qualifying its application in a mathematical optimising procedure. The influence of the latent heat released during the crystallisation phenomena was identified by the significant increase in heat load in the early stages of the freezing process. <![CDATA[<B>Swelling behavior of PEMFC during conditioning</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300010&lng=en&nrm=iso&tlng=en Polymeric cation exchange membranes (PEMFC) are used in fuel cell technology. These membranes act as a physical barrier between anode and cathode, but diffusion through the membrane should allow protons to be carried from anode to cathode at a rate sufficient to supply energy requirements. They avoid any direct reaction of oxygen and hydrogen that would diminish fuel cell efficiency. Membranes have to be conditioned before use. This conditioning step changes membrane counterions and modifies their water content, which has an effect on their diffusion coefficients. In order to analyse and quantify the effect of conditioning techniques on membrane performance various experiments with Nafion 117 cation exchange membranes were carried out. Membranes were conditioned using various methods to change the charged cation in the membrane. The reactives used were ultrapure water, nitric acid, hydrochloric acid, hydrogen peroxide, sodium chloride, potassium chloride and ethylene glycol, all at room temperature. Some conditioning methods were carried out using solvents heated to 100 ºC. Water content was indirectly monitored by measuring membrane swelling. Results show that membrane conditioning with strong acids followed by treatment with water increases membrane water content by about 5%. Using high-temperature treatment the water content also increases. Water uptake or release from membranes is analysed in terms of water activity. <![CDATA[<B>The elution of metal cyanocomplexes from polyacrylic - and polystyrene- based ion exchange resins using nitrate and thiocyanate eluants</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300011&lng=en&nrm=iso&tlng=en Ion exchange resins can potentially be applied in cyanide recycling to address growing environmental concerns over the use of cyanide during gold extraction. In the present work the elution of copper-, iron-, and zinc-cyanocomplexes from polyacrylic- and polystyrene-based resins was studied. It was found that iron and copper cyanides are easily eluted from polyacrylic- and polystyrene-based ion exchange resins using either SCN- or NO3-. However, elution of the zinc cyanide complex from polystyrene-based resins was poor when using nitrate solution as eluant. Besides, an increase in elution temperature from 25 °C to 50 °C improved the elution of iron and zinc cyanides from polystyrene-based resins using a nitrate eluant; however temperature did not have any significant effect on other metal cyanocomplexes or for elution using thiocyanate. It was therefore proposed that the optimal combination of resin-eluant was site-specific, and depends on the features of the effluent, processing temperature, eluant concentration, and ion exchange resin under consideration. <![CDATA[<B>Real-time process optimization based on grey-box neural models</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300012&lng=en&nrm=iso&tlng=en This paper investigates the feasibility of using grey-box neural models (GNM) in Real Time Optimization (RTO). These models are based on a suitable combination of fundamental conservation laws and neural networks, being used in at least two different ways: to complement available phenomenological knowledge with empirical information, or to reduce dimensionality of complex rigorous physical models. We have observed that the benefits of using these simple adaptable models are counteracted by some difficulties associated with the solution of the optimization problem. Nonlinear Programming (NLP) algorithms failed in finding the global optimum due to the fact that neural networks can introduce multimodal objective functions. One alternative considered to solve this problem was the use of some kind of evolutionary algorithms, like Genetic Algorithms (GA). Although these algorithms produced better results in terms of finding the appropriate region, they took long periods of time to reach the global optimum. It was found that a combination of genetic and nonlinear programming algorithms can be use to fast obtain the optimum solution. The proposed approach was applied to the Williams-Otto reactor, considering three different GNM models of increasing complexity. Results demonstrated that the use of GNM models and mixed GA/NLP optimization algorithms is a promissory approach for solving dynamic RTO problems. <![CDATA[<B>A novel hybrid optimization algorithm for diferential-algebraic control problems</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300013&lng=en&nrm=iso&tlng=en Dynamic optimization problems can be numerically solved by direct, indirect and Hamilton-Jacobi-Bellman methods. In this paper, the differential-algebraic approach is incorporated into a hybrid method, extending the concepts of structural and differential indexes, consistent initialization analysis, index reduction and dynamic degrees of freedom to the optimal control problem. The resultant differential-algebraic optimal control problem is solved in the following steps: transformation of the original problem into a standard nonlinear programming problem that provides control and state variables, switching time estimates and costate variables profiles with the DIRCOL code; definition of the switching function and the automatically generated sequence of index-1 differential-algebraic boundary value problems from Pontryagin’s minimum principle by using the developed Otima code; and finally, application of the COLDAE code with the results of the direct method as an initial guess. The proposed hybrid method is illustrated with a pressure-constrained batch reactor optimization problem associated with the slack variable method. <![CDATA[<B>The removal of dinitrochlorobenzene from industrial residuals by liquid-liquid extraction with chemical reaction</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300014&lng=en&nrm=iso&tlng=en Nitrochlorobenzenes (NCBs) are very important in the chemical industry since they have been used as raw material for the manufacture of crop protection products, as active ingredients in the pharmaceutical industry, as pigments and as antioxidants as well as for other uses. In industrial processes, NCBs are produced by monochlorobenzene (MCB) nitration reactions and one of the main residuals formed is dinitrochlorobenzene (DNCB), which is mainly composed of the isomer 2,4DNCB. This subproduct, although of commercial interest when in its pure state, is generally incinerated due to the high costs of recovery treatment and purification. The objective of this study is to present an alternative to the treatment of industrial residuals containing DNCB. The technique consists of converting DNCB into sodium dinitrophenolate, which is very soluble in water and is also easy to reuse. For this purpose, liquid-liquid extraction with chemical reaction (alkaline hydrolysis) with a rotating disc contactor (RDC) is used. Experimental data on MCB nitration reactions as well as alkaline hydrolysis using a rotating disc contactor are presented. <![CDATA[<B>Exergetic and economic analysis of an industrial distillation column</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322007000300015&lng=en&nrm=iso&tlng=en In this work, applications of exergy and economic concepts to compression, heat exchange, and separation processes were used for calculation of the irreversibility rate, thermodynamic efficiency, and internal rate of return (IRR) of the profitability. A case study based on a real process, the purification of 1,2-dichloroethane (DCE) in a high-purity distillation column, is presented. This column has the highest steam flow rate in any vinyl chloride monomer (VCM) plant. A configuration using a vapor compression heat pump is proposed for improvement of the energy efficiency without having to make important process modifications. Existing and proposed configurations were implemented using the Aspen Plus&trade; commercial simulator; the results of the existing configuration were validated with data extracted from the plant. The objective of this work was to compare the existing configuration with the proposed one, using a thermodynamic and an economic approach.